1. Field of the Invention.
The present invention relates generally to sound control systems and more particularly to a random noise masking system being dynamically and adaptedly responsive to a variety of inputs.
2. Description of the Prior Art.
Sound control of rooms in buildings have been known in the prior art to embrace a variety of separate component systems usually resulting in large economic waste and duplicated effort. An early type of sound control is the common paging system which utilizes a plurality of disposed loudspeakers being tied to a common amplifier which responds to a voice input on a remote microphone. Paging systems over the years have become more sophisticated and may actually induce noise into the page in order to reinforce the paging signal. See e.g., the A.A.A. Tomatis U.S. Pat. No. 3,101,391 issued Aug. 20, 1963. In addition, systems have been designed to raise the volume of the paging signal in response to an increasing level of background noise. See e.g., E. S. Seeley, U.S. Pat. No. 3,133,990 issued on May 19, 1964 and V. J. Meyers, U.S. Pat. No. 3,160,707 issued on Dec. 8, 1964.
Another common type of sound control is a music background system in which music is provided from a recording or the like into an amplifier for driving a plurality of spatially disposed speakers. Such systems have been known in the art to increase workers' productivity and to raise the morale of the environment. It is not uncommon, therefore, to find music systems which play a variety of renditions of different psychological moods at various intervals of time. The programmed music can be self-contained in a tape loop, or it can be brought in from an outside cable or antenna. Studies have shown that in general workers have a performance peak in the morning, and a reduction in performance after lunch, regardless of whether the lunch is eaten or not. Other studies have shown that the addition of background music can increase performance by modification of the program material, in particular, having the program more lively as time passes.
Another example of a prior art sound control system is a noise mask or speech privacy system. The purpose of a noise masking system is to provide a noise background that has a proper distribution of frequencies and amplitudes to effectively reduce interference associated with overheard speech, particularly in open spaces. With the development of large open spaces in buildings, which provide a great degree of space planning options, the speech interference of one worker with another creates a noise problem, as well as a loss of confidentiality. Such interference has been termed an "intrusion noise" that is the additional noise level above the normal room noise or "ambient level." Noise masking systems were developed to alleviate these difficulties by providing a series of loudspeakers in the ceiling plenum which are fed sequentially by a noise generator, a noise spectrum shaper and a power amplifier. The value of noise masking is so well recognized that one prior art approach discloses a portable noise generator for use in a variety of rooms and adverse ambient noise conditions. See e.g., T. G. Morrissey, U.S. Pat. No. 3,567,863 issued on Mar. 2, 1971. See also W. T. Cavanaugh, et al, "Speech Privacy in Buildings," 34 J. Acous. Soc. Amer. 475 (1962).
In the case of music and noise masking systems, the range of sound levels experienced by the workers must be never so low at any instant as to allow long range speech communication and never so high as to disrupt the workers' activity. More fundamentally, at the end of each day prior art paging, music or noise masking systems are not shut down.
Another type of sound control system is a security system in which a plurality of microphones are spatially disposed in the room or building and are interconnected into am amplifier for driving a detector circuit which, in the presence of an invasion noise, activates an alarm system. Such systems are generally only activated after working hours as a security measure.
The performance of a worker, however, depends on many more factors other than just the acoustical environment. Some of these factors, although very important, are not under the control of the building designer or operator and are not discussed here. The designer or operator, however, can control such environmental factors as sound, ionization level, light level, humidity and temperature. Studies have been conducted, and design rules and regulations are available which include these factors. Once these environmental factors are determined, they are implemented through building design, and generally they remain constant thereafter except for gross changes. For example, lighting levels in an office are constant until the lights are turned off in the evening. Some accommodations to changing conditions during work day have been made. For example, air conditioning systems can be designed so that as the temperature outside of a building goes up near mid-day, the inside temperature increases so that a differential remains constant. Such an accommodation reduces the thermal shock so often noticed when entering a cool building from an extremely warm outside. The improvements in building design can accommodate such changes in human comfort or attitudes during the work day, but most have not been made. The effect of background sound either through injecting masking noise or music into the room based on such factors is only beginning to become understood. Clearly background music or noise affects a person's attitude towards temperature, humidity, light level, ionization level and background noise level. However, no noise masking or music systems are adaptable to such environmental factors.
The major disadvantage of the above prior art sound control approaches is simply that economic waste is apparent through the duplication of amplifiers, loud speakers and other similar equipment. In addition, the prior art approaches are not variable either in spectral distribution or in amplitude with time throughout the day, but rather are constant throughout their application and certainly are not adaptable either to environmental factors or to the background noise of the building. For example, it is wellknown that in certain rooms disposed above nightclubs and bars, that throughout the better part of the day, the background noises substantially are at a minimum level. In the time interval from 9:00 P.M. to 2:00 A.M., however, substantial background noise may be apparent and may transmit upwardly and into the room. No prior art noise masking systems are preprogrammed to take into account this varying intrusion noise.
The present invention overcomes the above disadvantages by providing a completely random noise source for generating a plurality of different masking noises; by providing means for temporally and spatially varying the spectral distribution and adjusting the amplitude of the sound output in a plurality of speakers; by mixing paging commands, music and masking noise together in an aesthetically pleasing environment; by responding to various environmental factors with a predetermined mixture of masking noise and music; by making the transition between the various different temporal states slowly so as not to be consciously detected by persons in the room; by incorporating a security system into the noise and music system, and for manufacturing a low cost noise masking and music system.